Update include/cyclone/precision.h

Added definition of epsilons
Changed quaternion class /include/cyclone/core.h

It is rather unusual to have a perfect equality when comparing floating-point numbers. Thus it is necessary to compare with a margin, it being the machine epsilon. 

It is not needed to check against the abs of d, as it is made from (hopefully) positive numbers. If, by any chance, d<0, will be within machine error, and also caught by the current condition.
Merge pull request #16 from LucasCampos/master

Changed condition on which quaternion's length is zero.
Typo on include/cyclone/body.h

intertia -> inertia
Removed uneeded line on src/body.hpp

Removed isAwake = true; from addForceAtBodyPoint, as it will already be set to true on addForceAtPoint
Corrected calculations src/pfgen.cpp

Corrected some errors pointed in issue #11, first noticed by @SomeAdrian
Corrected bug include/cyclone/core.h. Issue #10

Inversion was not inverting z nor x correctly. Fixes issue #10, spotted by @integeruser
Merge pull request #17 from LucasCampos/master

Fixed issues #10 and #11, and some minor changes
Fixes typo on src/pcontacs.cpp. Issue #4

Fixes issue #4: Typo on line 52 of src/pcontacs.cpp. acelleration -> acceleration.
Fixes issue #19
Merge branch 'master' of https://github.com/LucasCampos/cyclone-physics
Merge pull request #20 from LucasCampos/master

Fixes issue#4. Typo on pcontacs.cpp